1. Field
This specification relates to a device and method for controlling a linear compressor.
2. Background
In general, a reciprocating compressor is configured in such a manner that a piston linearly reciprocates within a cylinder to suck, compress and discharge refrigerant gas, and more particularly, is classified into a recipro type and a linear type according to a method of driving the piston.
The recipro type is a method in which a crankshaft is coupled to a rotation motor and a piston is coupled to the crankshaft so as to convert a rotational motion of the rotation motor into a linear reciprocating motion. On the other hand, the linear type is a method in which a piston is directly connected to a mover of a linear motor so as to perform a reciprocating motion in response to a linear motion of the motor.
The linear type reciprocating compressor does not employ the crankshaft which converts the rotational motion into the linear motion, as aforementioned, so as to exhibit a low frictional loss and higher compression efficiency than general compressors.
When the reciprocating compressor is used for a refrigerator or an air conditioner, a compression ratio of the reciprocating compressor may be varied by varying a voltage input to the reciprocating compressor. This may allow for controlling a freezing capacity.
FIG. 1 is a block diagram of a driving control module of a general reciprocating compressor. A current detector 4 detects a motor current applied to a motor, and a voltage detector 3 detects a motor voltage applied to the motor. A stroke estimator 5 estimate a stroke based on the detected motor current and motor voltage and a motor parameter. A comparator 1 compares the stroke estimate with a stroke command value (or a stroke instruction value) to output a difference signal. A controller 2 controls the stroke by changing (varying) the voltage applied to the motor.
In operation, the current detector 4 may detect the motor current applied to the motor, and the voltage detector 3 may detect the motor voltage applied to the motor. Here, the stroke estimator 5 may calculate a stroke estimate by applying the motor current and motor voltage and the motor parameter to the following Equation 1, and apply the stroke estimate to the compressor 1.
                    X        =                              1            α                    ⁢                      ∫                                          (                                                      V                    M                                    -                  Ri                  -                                      L                    ⁢                                          i                      _                                                                      )                            ⁢              d              ⁢                                                          ⁢              t                                                          [                  Equation          ⁢                                          ⁢          1                ]            where R denotes resistance, L denotes inductance and a denotes a motor constant or a counter electromotive force constant.
The comparator 1 may compare the stroke estimate with the stroke command value and apply a thusly-obtained difference signal to the controller 2. The controller 2 may then control the stroke by varying the voltage applied to the motor of the linear compressor L-COMP. As illustrated in FIG. 2, the controller may reduce the voltage applied to the motor when the stroke estimate is greater than the stroke command value, and increase the voltage applied to the motor when the stroke estimate is smaller than the stroke command value.
Generally, a refrigerator as a home appliance runs for 24 hours. Among others, efficiency of a compressor may have the greatest influence on the power consumption of the refrigerator, and the efficiency of the compressor should be increased in order to reduce the power consumption of the refrigerator.
One of methods of increasing efficiency of a linear compressor may be to reduce a frictional loss. To reduce the frictional loss, an initial value of a piston (or an initial position at which the piston is located in a cylinder) may be reduced so as to decrease a stroke. However, the compressor efficiency and the maximum freezing capacity by the initial value of the piston may have a trade-off relationship.
The initial value of the piston is a factor which decides the maximum freezing capacity. The reduction of the initial value may result in an increase in the efficiency of the compressor based on the reduction of the frictional loss, but results in a reduction of the maximum freezing capacity and making it difficult to handle (manage) an overload.
Further, when the initial value is increased, the maximum freezing capacity of the compressor can be improved, but a moving distance (a distance between a top dead center (TDC) and a bottom dead center (BDC)) of the piston may be increased. This may cause an increase of a frictional loss and accordingly reduce efficiency of the compressor.
A top dead center is abbreviated as “TDC” and denotes a top dead center of the piston in the linear compressor. The TDC may physically indicate a stroke upon completion of a compression stroke of the piston. A point where the TDC is 0 (TDC=0) is simply referred to as ‘top dead center.’ Similarly, the bottom dead center is abbreviated as “BDC” and may physically indicate a stroke upon completion of a suction stroke of the piston.